Braking system for hybrid vehicle and control method for the same

Abstract

A braking system for hybrid vehicle may include a brake pedal, a pedal stroke sensor detecting stroke of the brake pedal and outputting corresponding signal, a brake control unit receiving the signal of the pedal stroke sensor, a driving wheel caliper braking a driving wheel according to control of the brake control unit, a regenerative braking unit including a motor/generator which generates electric energy according to control of the brake control unit in braking of the driving wheel, a master cylinder connected with the brake pedal and operated by the brake pedal, and a driven wheel caliper braking a driven wheel according to operation of the master cylinder.

What is claimed is: 
     
       1. A braking system for a hybrid vehicle comprising:
 a brake pedal; 
 a pedal stroke sensor detecting a stroke of the brake pedal and outputting a corresponding signal; 
 a brake control unit receiving the signal of the pedal stroke sensor; 
 a driving wheel caliper braking a driving wheel according to control of the brake control unit; 
 a regenerative braking unit including a motor/generator generating electric energy according to control of the brake control unit in braking of the driving wheel; 
 a master cylinder connected with the brake pedal and operated by the brake pedal; and 
 a driven wheel caliper braking a driven wheel according to operation of the master cylinder, 
 wherein the brake control unit determines a required braking force based on the signal of the pedal stroke sensor, 
 wherein the brake control unit determines a braking force of the driving wheel by subtracting a braking force of the driven wheel from the required braking force determined based on the signal of the pedal stroke sensor, and 
 wherein the brake control unit controls operations of the driving wheel caliper and the regenerative braking unit based on the determined braking force of the driving wheel, 
 wherein when a value determined from subtracting a regenerative braking force from the braking force of the driving wheel is larger than zero, the brake control unit controls operation of the driving wheel caliper based on the value of the regenerative braking force of the regenerative braking unit subtracted from the braking force of the driving wheel, and 
 wherein the brake pedal has a predetermined dead stroke and the braking force of the driven wheel is “0” in the predetermined dead stroke of the brake pedal and only the regenerative braking unit is operated in the predetermined dead stroke. 
 
     
     
       2. The braking system of  claim 1 , wherein the brake control unit determines the regenerative braking force according to multiplying current torque of the motor/generator by gear ratio of a shift range. 
     
     
       3. The braking system of  claim 2 , wherein the brake control unit determines an efficiency of the motor/generator by assuming torque of the motor/generator, and the brake control unit compares the efficiency of the motor/generator with a predetermined efficiency of a standard motor/generator for regenerative braking in order to determine the shift range. 
     
     
       4. The braking system of  claim 1 , further including:
 a wheel control unit which is operated by hydraulic pressure of the master cylinder and controls operation of the driven wheel caliper by hydraulic pressure. 
 
     
     
       5. A control method of controlling a braking system for a hybrid vehicle, comprising:
 determining, by a brake control unit, a first braking force of a driven wheel when a brake pedal is operated; 
 determining, by the brake control unit, a required braking force when the brake pedal is operated; and 
 determining, by the brake control unit, a second braking force of a driving wheel by subtracting the first braking force of the driven wheel from the required braking force; 
 wherein the braking system includes:
 the brake pedal; 
 a pedal stroke sensor detecting a stroke of the brake pedal and outputting a corresponding signal; 
 the brake control unit receiving the signal of the pedal stroke sensor; 
 a driving wheel caliper braking the driving wheel according to control of the brake control unit; 
 the regenerative braking unit including a motor/generator generating electric energy according to control of the brake control unit in braking of the driving wheel; 
 a master cylinder connected with the brake pedal and operated by the brake pedal; and 
 a driven wheel caliper braking the driven wheel according to operation of the master cylinder, 
 
 wherein the brake control unit determines the required braking force based on the signal of the pedal stroke sensor, 
 wherein the brake control unit determines the second braking force of the driving wheel by subtracting the first braking force of the driven wheel from the required braking force determined based on the signal of the pedal stroke sensor, 
 wherein the brake control unit controls operations of the driving wheel caliper and the regenerative braking unit based on the second braking force of the driving wheel, 
 wherein when a value determined from subtracting a regenerative braking force from the second braking force of the driving wheel is larger than zero, the brake control unit controls operation of the driving wheel caliper based on the value of the regenerative braking force of the regenerative braking unit subtracted from the second braking force of the driving wheel, and 
 wherein the brake pedal has a predetermined dead stroke and the first braking force of the driven wheel is “0” in the predetermined dead stroke of the brake pedal, and only the regenerative braking unit is operated in the predetermined dead stroke. 
 
     
     
       6. The control method of  claim 5 , wherein the braking of the driving wheel is executed by operating the regenerative braking unit when the value which is determined from subtracting the regenerative braking force from the second braking force of the driving wheel is less than “0”. 
     
     
       7. The control method of  claim 6 , wherein the braking of the driving wheel is executed by operating both of the regenerative braking unit and the driving wheel caliper when the value which is determined from subtracting the regenerative braking force from the second braking force of the driving wheel is equal or larger than “0”. 
     
     
       8. The control method of  claim 5 , wherein the regenerative braking force is determined by multiplying current torque of the motor/generator by gear ratio of a shift range. 
     
     
       9. The control method of  claim 8 ,
 wherein an efficiency of the motor/generator is determined by assuming a torque of the motor/generator; and 
 wherein the determined efficiency of the motor/generator and a predetermined efficiency of a standard motor/generator for regenerative braking are compared in order to determine the shift range. 
 
     
     
       10. The control method of  claim 9 ,
 wherein a current shift range is maintained when the determined efficiency of the motor/generator is equal to or larger than the predetermined efficiency of the standard motor/generator for regenerative braking; and 
 wherein the current shift range is lowered when the determined efficiency of the motor/generator is less than the predetermined efficiency of the standard motor/generator for regenerative braking.